This invention relates to cassettes for containing an inked ribbon for use in printing mechanisms such as are used for printing the data output of computers for example.
One known form of ribbon cassette consists of a housing containing a quantity of inked ribbon held in closely packed loops with guides extending from the housing for guiding the ribbon to and from a printing position in which it passes between a printing element and a paper web or sheet on which printing is to be effected. The ribbon is in the form of an endless loop and is pulled from the housing by engagement between a feed roll/gear and an idler roll/gear. The ribbon emerging from the rolls is then fed back into the housing. The ribbon may be fed past the printing position a number of times before the ink available from the ribbon is insufficient to effect a clear print impression on the paper. When the ribbon is no longer useful, the cassette must be removed from the printing mechanism and replaced by a new cassette containing a ribbon fully charged with ink. Whenever the cassette needs to be replaced the printing mechanism has to be stopped to enable the old cassette to be removed and a new cassette to be fitted. Hence it is desirable that the cassette should contain the largest practicable quantity of ribbon in the housing so that the cassettes do not require to be replaced too frequently. However there are practical limits on the overall size of cassette which can be accommodated on a printing mechanism. Furthermore friction between the tightly packed folds of ribbon and the walls of the housing results in the need to restrict the total length of ribbon contained in the cassette housing in order to ensure that the force required to draw the ribbon from the housing is not so large that the ribbon could be subjected to fatal damage, stretching or slipping in the drive roll/gear.